Hydraulic Transients Research Articles

An accurate and efficient scheme involving unsteady friction for transient pipe flow

Abstract A robust prediction system should monitor all possible hydraulic transients, which is significant for the appropriate and safe operation of pipe systems. A second-order finite volume method (FVM) Godunov-type scheme (GTS) considering unsteady friction factors is introduced to simulate hydraulic transients, which was rarely involved in previous work. One explicit-solution source item approach developed in this work is crucial for the proposed GTS to easily incorporate various forms of the existing unsteady friction models, including original convolution-based models (Zielke model and Vardy–Brown model), simplified convolution-based model (Trikha–Vardy–Brown (TVB) model), and Brunone instantaneous acceleration-based model. Results achieved by the proposed models are compared with experimental data as well as predictions by the classic Method of Characteristics (MOC). Results show that the MOC scheme may produce severe numerical attenuation in the case of a low Courant number. The proposed second-order GTS unsteady friction models are accurate, efficient, and stable even for Courant numbers less than one and sparse grid, and only need much less grid number and computation time to reach the same numerical accuracy. The TVB convolution-based model and Brunone model in the second-order GTS are suggested for further applications in hydraulic transients due to their high accuracy and efficiency.

Hydraulic Design Challenges of High Head 880 MW Gouvães Pumped-Storage Power Plant

The 880 MW pumped-storage power plant of Gouvães, which is part of the Alto Tâmega hydro power scheme from Iberdrola is currently under construction in the north of Portugal. The power plant is equipped with 4 reversible Francis pump-turbines with a gross head of 660 m. The power plant features several challenges with respect to the hydraulic design such as: i) ultra-high-head single stage reversible Francis pump-turbine of very low specific speed leading to severe hydraulic transients, ii) a long high-pressure penstock, iii) an headrace differential surge tank linked to a 4700 meters long headrace tunnel and iv) a complex tailrace differential surge tank linked to a 700 meters long tailrace tunnel. To perform the hydraulic design of the pumped-storage power plant, a stepwise approach presented in the paper was undertaken by Iberdrola. A detailed 1D hydraulic transient analysis was performed to optimize the headrace and tailrace surge tank dimensions. Then a combined CFD and reduced scale physical transient tests of both surge tanks was conducted. This enabled to address the complex 3D flow physics that develop in surge tanks but are not captured by 1D transient simulations such as free surface, upsurges against walls, verification of throttle singular head losses and effects not captured by 3D CFD such as air-water mixture and detection of air entrainment risk.

The Effect of Different Transient Trigger Methods on the Performance of Double Controlled Hydraulic System

Most of pressurized liquid pipelines are threatened by the hazards of a physical phenomenon that likely occurred in the hydraulic system when flow characteristic is rapidly changed. This change will make local energy imbalance which induced pressure wave travelling along the hydraulic system. Further, many devices are designed to control the hydraulic transients event. But, these devices still have incomplete performance because they dont be verified under different transient trigger conditions. In this paper, the performance of double controlled hydraulic system is verified by changing the transient trigger methods. Where, the double control of this system consisting of air vessel and HDPE forward configuration bypass. Moreover, four transients trigger scenarios are performed in this study and the performance of the hydraulic system for each scenario is investigated experimentally and numerically. Further, the experiments are revealed that the performance of hydraulic control system is highly affected by the way of the hydraulic transient is generated. Finally, the experimental and numerical results are well convergent by a total percentage is (92%).

WITHDRAWN: Viscoelastic loop strategy for water hammer control in a pressurized steel pipeline

Abstract The challenges of water hammer phenomenon impose many technical and economic barriers to the design and operation of the pressurized hydraulic systems. So the objective of most literature in this field was finding an applicable strategy that was capable to suppress the threatening of hydraulic transient and fulfill the required technical and economic limits of the project. In this paper, an experimental investigation is presented to verify the effectiveness of the viscoelastic loop strategy to control and damp the water hammer triggered in the pressurized pipeline due to pump’s trip or downstream valve closure. This strategy comprises two viscoelastic bypass pipes are configured to form a counter clockwise loop that allow to the flow in certain direction and restrain its opposite one. On the other hand, the performance of viscoelastic loop strategy is compared to the classical air vessel device to control the induced hydraulic transients. Further, the experimental results revealed the viscoelastic loop strategy is very effective to control the water hammer with overall maximum pressure damping efficiency reaches to (69.5%). Furthermore, the viscoelastic loop strategy is superior to the classical air vessel device for different transients trigger conditions in the most cases of the experiments.

Numerical simulation of hydraulic transients in hydropower station with complicated water conveyance system

With the construction of Jinping II hydropower station with extra-large diversion tunnel, Baihetan hydropower station with complicated tailwater system, Yangfanggou hydropower station with complicated surge chamber, High requirements are put forward for the calculation and analysis of hydraulic transient process. In the water transmission and power generation system design of these projects, the following technical problems was solved by Power China Huadong Engineering Corporation Limited: simulation of variable impedance coefficient of differential surge chamber, interface tracking analysis of free-surface-pressure flow system, narrow upper chamber open channel effect and simulation of trigeminy surge chamber. The solutions to those technical problems and were summarized, and the hydraulic transients simulation and calculation software of complex waterway system - Hysim was developed. Based on the field test of Jinping II Hydropower Station, Baihetan hydropower station and Yangfanggou hydropower station, the simulation calculations were carried out. The accuracy of the hydraulic transients simulation software is verified by comparing the inversion results with the test values.

Numerical Simulation Study on Hydraulic Transients in Hydropower Station with Trigeminy Surge Tank

A static and dynamic model for hydraulic transient calculation of three-throttled-orifice surge tank was established based on the basic equations of surge tank, by using structure matrix method (matrix analysis of structure?). Control conditions in an engineering practice were calculated by a simplified model and a three-throttled-orifice model respectively. The results indicate that the maximum pressure at the volute end, the maximum rising rate of unit speed and the water level extremum of the surge tank are basically identical by using these two models, but the minimum pressure at draft tube inlet is significantly different. The three-throttled-orifice model was found capable of calculate the flow between throttled orifices at constant state and the pressure behavior at draft tube inlet during the transition accurately. The selection of the resistance factor is discussed in the end, and it is proved that the resistance factor is allowed to have a certain tolerance in the transition calculation, which will not obviously affect the maximum pressure at draft tube inlet and water level extremum of the surge tank. This research can provide reliable reference for the transient calculation of three-throttled-orifice surge tank in similar engineering practice.

빗물펌프장의 수력학적 과도현상에 관한 연구

In this study, a field test was conducted to study the water hammer, which is a hydraulic transient phenomenon occuring at a rainwater pumping station. The drainage pump subject to the field test was a vertical shaft two floor mixed flow pump with a pump bore of 2,000 mm and a motor power of 1,320 kW. To test the hydraulic transients phenomenon of the drainage pump, the pressure sensors were installed on the pump discharge side and the outlet of the check valve. In the electrical transient test, the voltage, current, and the power facter of the motor were measured using a power meter. The measured pressure and electrical values were stored in a data acquisition system. A field test for water hammer phenomenon that occur when starting and stopping the drainage pump were conducted in cases where the electric butterfly valve was throttled and when it was full open. As a result of the field test, it was analyzied that the method of cutting off the power of the drainage pump after significantly throttling the electric butterfly valve can reduce the flow velocity in the discharge pipe, but the effect of increasing the pressure of the drainage pump appeared greater. It was observed that the flap valve closed before the check valve when the power to the drainage pump was shut off, and when the flap valve closed abruptly 1 second before and after, slamming occurred. This may cause the valve disk and the valve seat to be damaged by the impact, therefore, caution is required.

Effect of an entrapped air pocket on hydraulic transients in pressurized pipes

The current research focuses on the analysis of different dynamic effects of an air pocket located at mid-pipe length on transient pressures based on experimental data. Different flow rates and air pocket volumes are analysed. Several features are identified in the pressure-head signal associated with the air pocket: initial pressure drop, higher maximum overpressure peaks, increased pressure wave damping and delay. These features result from the superposition of pressure waves associated with the entrapped air contraction and expansion. Smaller air pockets generate minor reflections, whereas larger air-pockets tend to disperse and artificially attenuate maximum pressures. Video recording images of the air pocket during the transient event allow observation of two types of behaviour: one associated with lower transients, characterized by an air pocket volume variation with a clear air–water interface; and another one associated with more severe transients in which air mixes with water. Finally, there is a critical air pocket volume, independent of the initial flow rate, that leads to the highest overpressures.

Field Measurements and Numerical Modeling of Hydraulic Transients in HDPE Pipeline with PRV Interaction

Pressure reducing valves (PRVs) and high-density polyethylene (HDPE) pipes are commonly used in urban water supply systems (UWSS). To study the joint effect of PRV and viscoelasticity on transient wave propagation, extensive experiments have been conducted in a field-scale reservoir-PRV-viscoelastic pipeline system covering a wide range of internal pressure heads (∼10 to 60 m) and air temperatures (12°C–33°C). In addition, a one-dimensional method of characteristics (MOC) based model that incorporates a PRV model and the generalized Kelvin-Voigt (K-V) model for pipe viscoelasticity is developed and validated against field data for the first time. The simulated transient pressures are in good agreement with field measurements. The K-V parameters exhibit a clustered distribution and the mean value for each element can provide a satisfactory simulation. The PRV in hydraulic transients can be interpreted as a quasi-dead-end with a self-adjusting opening, and causes additional positive pressure wave reflections that are gradually damped due to viscoelasticity. The dynamic changes in PRV opening, head loss, pressure wave reflection, and transmission induced by an incident pressure surge are predicted. Due to the joint action of PRV and pipeline viscoelasticity, the pressure oscillations in an intact pipe settle to a value that is considerably higher than the initial PRV set pressure. In a leaking pipe, the downstream pressure reverts to the original set pressure within a few wave cycles. Leaks can be detected by wave reflections in the time domain signals. The existence of leaks is also found to be associated with the the amplification and damping of the frequency response function (FRF) of the system at certain resonance peaks. This study provides new insights into wave propagation in HDPE pipeline with PRV interaction and an original data set for validation of leakage detection methods.

Numerical study on the transient behavior of a radial pump during starting time

Abstract This paper presents a fast simulation model for predicting the dynamic response of a motor-pump system to startup event. The purpose is to analyze the effect of the impeller acceleration time, the final flow rate and the impeller geometry on the pump transient flow during starting operations. The motor speed and torque variations were predicted by simulating the transient law of the three-phase induction motor by adopting the d-q axes theory. The pump model was built by solving the unsteady flow governing equations with the method of characteristics (MOC). The whole model was validated with available tests from literature. Accordingly, the computation of impeller acceleration, the motor torque, the unsteady pressure and flow rate was made for various starting conditions. The results have revealed that during its starting time, the pump hydraulic transients are well influenced by the motor speed acceleration, the flow inertia and the impeller geometry. Through the analysis of the simulation results, the conclusion was that the accuracy of the present method is reasonable, and it can be used for assisting pumping system design.

A 30‐year review of copper pitting corrosion and pinhole leaks: Achievements and research gaps

AbstractDespite decades of research, the pitting of copper pipes is poorly understood. This article summarizes the key research findings from 1990 to the present and identifies research gaps. Several lines of evidence suggest that, for soft waters, additional alkalinity or maintaining a pH <8.5 may reduce copper pitting. Phosphate corrosion inhibitors, used to prevent lead corrosion, may also moderate copper pitting in low‐alkalinity waters. However, such inhibitors could also exacerbate pitting due to insufficient coverage or could increase biological growth. Biological processes are likely involved in pitting corrosion, and practices to reduce biological growth may be beneficial. The research gaps identified include a need for better benchmarking, the effects of chemical transients (e.g., chlorine burns) and of hydraulic transients (e.g., water hammer), and changing the residual disinfectant from chlorine to chloramine.Article Impact StatementApproximately 750,000 pinhole leaks are estimated to occur in the United States each year, but we do not really know why.

Application of the shock response spectrum method to severity assessment of water hammer loads

Water hammer (WH) is a transient phenomenon which happens to appear in pipe flow systems as an effect of a sudden change in pipe flow conditions. Various origins can be the primary source of WH. They usually come from the liquid (e.g. operation of valves), but when the pipeline system is significantly elastic, WH can be produced by an external impact or transient vibration due to fluid structure interaction (FSI) effect. Hydraulic transients are usually undesired effects as large amplitudes of pressure waves, pipe stresses or vibration accompanying this phenomenon can be the source of pipeline system malfunction. Therefore, many efforts are taken by scientists and engineers to avoid unexpected WH events or to reduce their harmfulness. Systematic protection of pipeline systems requires a reliable method of severity estimation of WH loads. Various ways can be used for evaluation of WH strength. In general, severity of a transient depends on its amplitude, i.e. the maximum value of the liquid pressure. Another important factor is time dependence of the load signal however, a simple observation of its shape in time domain is usually not an effective technique. Instead, frequency domain analysis can be exploited. A specific kind of spectral analysis used in structural mechanics for assessment of shock loads and transients is the shock response spectrum (SRS) method. An original concept of application of this technique to WH events is proposed in this study. The method is shortly presented and its numerical approach developed by the author and applicable to WH loads are described. As an example of use the SRS computations and analysis of own WH experimental results measured at a laboratory pipeline are performed and concluded. Specific preprocessing of WH signal was applied and explained. It is evidenced in the paper that the applied SRS method gives a valuable and effective tool for determination of WH load severity. Therefore, it can also be used for comparison between alternative designs of pipeline system applied for protection from undesired WH events.

An experimental study of how hydraulic transients cause mobilisation of material within drinking water distribution systems

This paper provides new insight into how the hydraulic transients that occur within drinking water distribution networks can mobilise material adhered to the pipe wall and hence cause unacceptable water quality and customer dissatisfaction. Results are reported from extensive, representative, physical experiments covering a wide range of repeatable rapidly accelerating and decelerating hydraulic conditions. Novel time synchronous analysis shows that mobilisation always occurs in the first dynamic surge of the transient; however, differences in the physical processes that govern mobilisation were observed between the two groups of transient type studied. A function to estimate the mobilising force is proposed and applied to the physical experiments performed. The research provides important insights for identifying and understanding the mechanisms and forces induced during transients, vital for ensuring the supply of safe drinking water in operational distribution systems.

Research and Application on Numerical Simulation of Hydraulic Transients in Complex Water Conveyance System

Accurate simulation of hydraulic transients is crucial and complicated in the design of hydropower station and pumped storage power station. In this paper, key technologies for hydraulic transient simulation calculation in complex water conveyance system were studied. The structural matrix method with advantages of high accuracy and fast speed for numerical calculation was introduced. Complicated elements in the conveyance system were refined, such as high precision simulation of differential surge chamber, simulation of long and narrow upper chamber, new interpolation method for characteristic curve of pumped storage unit. Based on Jinping II hydropower station with special long headrace system and differential surge chamber, Baihetan hydropower station with complex tailrace system and large surge chamber and Xianyou pumped storage power station with complex unit characteristics and various working conditions, the application of the simulation software HYSIM in field test and inversion calculation was illustrated. The paper providing references for the design of similar projects.

Suppression of hydraulic transients for desalination plants based on active control synthesis

AbstractThis paper proposes a control strategy to stabilize a reverse osmosis desalination system against hydraulic shocks with enhancing productivity and sustainability. First, the effects of hydraulic transients on water quality have been reviewed. The transient waves are approximated by sinusoidal functions so that their effects are incorporated into the controlled system as external disturbances. Next, the active control is implemented based on the adaptive super-twisting (STW) sliding mode control (SMC) algorithms. Then, the robust performance is guaranteed whenever the sliding variables reach the sliding surfaces in finite time despite disturbances. The STW SMC scheme is to eliminate the chattering problems for protecting the valves and to improve the convergence precision for water production. The control gains are adaptable to enable formation of an effective controller for dealing with large disturbances such as water hammer during desalination process. The simulation results reveal the superior performances on controlling water product, while eliminating shock waves. Especially, the effect of hydraulic shocks has been dramatically attenuated, hence the plant components are protected to avoid fracture. Finally, the robust stability and performance of the desalination plants are guaranteed against large disturbances to ensure the population with quality water as well as system sustainability.

Stress-Informed Control of Medium-Head Hydropower Plants to Reduce Penstock Fatigue

The displacement of conventional generation in favor of stochastic renewable requires increasing regulation duties from the remaining dispatchable resources. In high- and medium-head hydropower plants (HPPs), providing regulation services to the grid and frequently changing the plant's set-point causes water hammer, which engenders pressure and stress transients within the pressurized conduits, especially the penstock, damaging it in the long run. This paper proposes a model predictive control (MPC) that explicitly models the hydraulic transients within the penstock. It achieves to reduce the mechanical loads on the penstock wall, and, consequently, fatigue effectively. Thanks to a suitable linearization of the plant model, the optimization problem underlying the MPC scheme is convex and can be solved with off-the-shelf optimization libraries. The performance of the proposed controller is tested with numerical simulations on a 230MW medium-head HPP with Francis turbine providing primary frequency control. Simulation results show substantially reduced penstock fatigue, existing approaches outperformed, and problem resolution times compatible with real-time control requirements.

Real-time neuro-fuzzy controller for pressure adjustment in water distribution systems

Abstract This work applied a neuro-fuzzy technique for real-time pressure control in water distribution systems with variable demand. The technique acted to control the rotation speed of the pumping system, aiming mainly at increasing energy efficiency. Fuzzy, neural and neuro-fuzzy controllers were tested in an experimental setup to compare their performances in a transient regime, a permanent regime, and with respect to disturbances applied to the system. To evaluate the efficiency of the system, a demand variation curve was emulated for different operating conditions. The results demonstrate that the neuro-fuzzy controller (NFC) presented a significant increase in pumping system efficiency and a reduction in specific energy consumption of up to 79.7% when compared to the other controllers. Target pressures were kept close to the set-point values with low hydraulic transients and maintained satisfactory stability (error <8%) under severe situations of demand variation. It is concluded that the NFC presented superior results when compared with the other analyzed controllers.

Transient flow simulation, analysis and protection of pipeline systems

This paper investigated the problems and impacts of transient flow in pipeline systems due to pump power failure. The impact of different protection devices was presented to assure surge protection for the pipeline system. A model via Bent-ley HAMMER V8.0 Edition was employed to analyse and simulate hydraulic transients in the pipeline system, and protec-tion alternatives were studied. Surge protection included using only an air vessel, using an air vessel and two surge tanks, and employing five air ves-sels and vacuum breaker. The obtained results for pressures, heads, and cavitation along the pipeline system were graph-ically presented for various operating conditions. Using five air vessels with vacuum breaker valve as surge protection proved to be more effective and economical against pump power failure. Changing the flow density did not have a significant impact on the pressures. For protection with an air vessel; it was concluded that the value 40% of the original diameter for inlet pipe diameter of air vessel, and the value of 2/3 of original pipe diameter were critical values for the transient pressures. Cast iron pipes proved to be the best pipe material for all studied volumes of the air vessel. For protection with an air vessel and two surge tanks; as the inlet pipe diameters increased the maximum pressures in-creased and the minimum pressures decreased. Regression analyses were performed obtaining equations to predict the pressures according to the inlet pipe diameter, the area of surge tank, and the pipe diameter.

A Review of Critical Stable Sectional Areas for the Surge Tanks of Hydropower Stations

The critical stable sectional area (CSSA) for surge tanks corresponds to the critical stable state of hydropower stations and is an important index to evaluate the stability of the turbine regulation system. The research on CSSA for surge tanks is always one of the most important topics in the area of transient processes of hydropower stations. The CSSA for surge tanks provides the value basis for the sectional area of surge tanks. In engineering practice, the CSSA for surge tanks is widely used to guide their hydraulic design. This paper provides a systematic literature review about the CSSA for surge tank of hydropower stations. Firstly, the CSSA for surge tanks based on hydraulic transients is discussed. Secondly, the CSSA for surge tanks based on hydraulic-mechanical-electrical coupling transients is presented. Thirdly, the CSSA for air cushion surge tanks is illustrated. Finally, the CSSA for combined surge tanks, i.e., upstream and downstream double surge tanks and upstream series double surge tanks, is presented. In future research, the CSSA for surge tanks of pumped storage power stations should be explored. The CSSA for surge tanks considering multi-energy complement is worth studying.

Wave celerity in hydraulic transients computation for CIPP-rehabilitated pipes

Wave celerity in hydraulic transients computation for CIPP-rehabilitated pipes